The present invention relates in general to devices for singling out flat objects, such as pieces of mail, and in particular to a new and useful device for removing one flat object at a time from a stack of flat objects.
A device of this kind is known from the Werner Frank et al U.S. Pat. No. 4,077,620 which issued Mar. 7,1978 for APPARATUS FOR THE SUCCESSIVE RELEASE OF ITEMS OF MAIL FROM A STACK. That patent discloses a device for successively dispensing a singled out letter from a stack of letters which includes a drawoff member that is continuously in engagement with a foremost letter of the stack, and which revolves in a continuously controlled manner to advance letters into a pickup zone. A pair of continuously driven transport rollers are provided in the pickup zone for further advancing the letter. A first sensing device is arranged between an exit for the stack and the transport rollers.
This is followed by a second sensing device at a given distance from the first. A control circuit controls the drive of the drawoff member as a function of the signals of the sensing devices. Both sensing devices form measuring sections extending along the transport path, the output signals of which are a measure of the partial section of the respective measuring section traveled by the front edge of the letter to be dispensed or respectively by reference edge of the previously dispensed letter. The control circuit is designed so that the drive of the drawoff member sets in as soon as the partial section of the second measuring section traveled by the reference edge of the previously dispensed letter has become co-extensive with the partial section by which the letter to be dispensed protrudes into the first measuring section. Preferably the sensing devices consist of the light barriers.
In other words, the known separating or "singling" device triggers a drawoff when, by means of the sensing devices (light barriers), it is established that a given minimum distance is reached between the trailing edge of the preceding letter and the leading edge of the following letter.
This given minimum distance must in practice be given so that devices connected after the singling device, e.g. a letter sorting device, can process as many letters as possible per unit time. Trouble-free processing requires the maintenance of minimum gaps between successive letters.
Adversely affecting the actual maintenance of these minimum gaps are the different mechanical properties of the letters which are not completely alike e.g. in dimension, weight and surface roughness etc., because by the acceleration process by the triggering of their drawoff from the stack in the case of such different letters, gap enlargements as against the optimum minimum gap are the consequence. This results in a reduction of the processing performance per unit time since in the majority of cases, the letters do have different dimensions or weights.